In typical cellular applications, an active subscriber identity needs to be registered in a corresponding network to be able to perform communication via the network. Such communication may, for example, comprise initiating and receiving calls, SMS (short message service) and the like. Thus, an aim of performing a registering procedure (e.g. signaling procedure towards the network (attach procedure, location update, muting area update, etc.) towards a network is to inform the network that the mobile terminal associated with the subscriber identity is switched on and is able to receive paging and other messages from the network.
When a subscriber identity performs a de-registration from a network, a purpose is to inform the network that the mobile terminal associated with the subscriber identity is switched off and, hence, that paging and other messages should not be transmitted/broadcasted anymore.
A registered subscriber identity may also perform update procedures towards the network at defined moments in time.
This may for example be the case when the location of the mobile terminal has changed.
Another example is that a typical network may require a registered subscriber identity to perform a periodic update procedure towards the network to confirm its active status (and possibly its location).
Typically, the network maintains a timer for this purpose. The timer is reset whenever a subscriber identity performs a registration or update procedure. If the tinier expires, the network typically considers the subscriber identity as de-registered. This has the advantage that the network will not waste efforts in trying to reach a subscriber identity that has become un-reachable without having performed the de-registration procedure (e.g. due to loss of coverage, low battery, battery removal, etc.). A typical timer setting may be that it expires after approximately 6 hours or more than 6 hours. The example timer T3212 in 3GPP specification TS24.008 has an expiry setting of 6 hours.
A corresponding timer (typically shorter than the network timer) is maintained in the mobile terminal for the subscriber identity. This timer is also reset whenever a subscriber identity performs a registration or update procedure. When the timer expires, a periodic update procedure for the subscriber identity should typically be initiated by the mobile terminal. Examples of such timers are the timers T3212 and T3312 in 3GPP specification TS24.008. The timer duration value(s) may typically be either strictly defined in an applicable standard or broadcast by the network (e.g. in a System Information signaling). The timer maintained in the mobile terminal for the subscriber identity typically has a timer duration value that is directly related to the timer duration value of the corresponding timer maintained in the network.
Typically, the periodic update timer of a subscriber identity is running in the terminal only for a subscriber identity which is currently active (e.g. served by a stack). The timer may be kept running even during e.g. loss of coverage. Thereby, a subscriber identity gaining coverage again may be able to determine if the network has de-registered it or not.
Related to a subscriber identity, a corresponding context is maintained in the network for that particular subscriber identity. The context may, among other things, maintain information regarding the status of the subscriber identity (e.g. registered or de-registered) and location information of the subscriber identity (e.g. home location and temporary location, such as local temporary identity—TMSI (temporary mobile subscriber identity)/P-TMSI (packet temporary mobile subscriber identity)). Some information of the context may be always maintained (e.g. status and home location), while other information may only be maintained while the subscriber identity is registered (e.g. temporary location).
The context is updated when a subscriber identity is registered, updated and/or de-registered in the network. The context may also be updated at other times.
Due to this context, the network is able to know if a particular subscriber identity is able to receive messages (e.g. paging) or not, and at which location the network should transmit the messages.
A DSDS (dual SIM dual standby) phone is equipped with two subscriber identity means (e.g. two SIM sockets and two copies any hardware directly associated with the SIM sockets). It is adapted to be able to receive paging messages and perform necessary measurements for both subscriber identities if they are both in idle mode. However, as soon as one of the subscriber identities enters a connected mode, the DSDS phone is typically not able to attend to the other subscriber identity. For example, a DSDS phone may have dual SIM software stacks and associated hardware architecture, but only one baseband processing unit and radio frequency unit.
When one subscriber identity is performing communication, the other subscriber identity is typically not reachable from the network point of view. Thus, no communication can be performed for the other subscriber identity.
A DSDC (dual SIM dual connected) phone is also equipped with two subscriber identity means (e.g. two SIM sockets and two copies any hardware directly associated with the SIM sockets). It is also adapted to be able to receive paging messages and perform necessary measurements for both subscriber identities when they are in idle mode. However, when one of the subscriber identities enters a connected mode, the DSDC phone is still able to attend to the other subscriber identity (e.g. performing measurements and listen to pages). For example, a DSDC phone may have dual SIM software stacks and associated hardware architecture, and also dual baseband processing units and radio frequency units.
From a user perspective, a dual SIM phone provides the possibility to use two different subscriber identities in one single device without having to perform a physical subscriber identity module exchange.
The behavior towards the network of dual SIM phones (e.g. DSDS or DSDC) is not specified in any standard. Typically, single subscriber identity device behavior is adopted by default.
For a single subscriber identity device (e.g. a single SIM phone), the registration procedure is typically performed at power on and the de-registration at power off.
For a dual or multiple subscriber identity device in which the multiple subscriber identities may be simultaneously active at least in idle mode (e.g. a DSDS phone or a DSDC phone), registration/de-registration/update procedures may typically also be performed at other times than power on/off.
The registration, update and de-registration processes takes some time. In an example scenario, the de-registration/registration processes typically take approximately 8 seconds.
If several registration/update/de-registration procedures are performed in sequence, there is a risk of signaling overload towards the network. Naturally, a situation of signaling overload should preferably be avoided.
Naturally, the operations performed and the signaling involved in association with registration/update/de-registration also consumes power.
These problems are experienced in both single and multiple subscriber identity devices. Some problems are typically more pronounced in multiple subscriber identity devices (since, there is typically more registration/de-registration/update procedures performed in such devices), for example the delay problem.
Therefore, there is a need for improved methods and arrangements for multiple subscriber identity scenarios of a communication terminal.